| With the rapid development of high-speed railways in our country,some major technical issues related to the safe operation of high-speed trains have emerged.Among them,the wheel polygonal wear is one of the most prominent technical problems.The wheel polygonal wear refers to the wavy wear along the circumferential direction of the tread,which will change the geometric relationship between the wheel and rail,produce a fixed wheel-rail contact irregularity,and affect the dynamic performance of vehicles seriously.In the dissertation,the frictional self-excited vibration models of wheelset-track systems are established based on the viewpoint of the frictional self-excited vibration ducing the wheel polygonal wear.The analysis methods include the complex eigenvalue analysis method and the transient dynamic analysis method.The mian conclusions can be summarized as follows:(1)Based on the viewpoint of the frictional self-excited vibration ducing the wheel polygonal wear,the finite element model of a high-speed wheelset-track system is established according to actual railway operating parameters,and the motion stability of the wheelset-track system is studied.The results show that when the creep force between the wheel and rail becomes saturated,it is found that frictional self-excited vibration of the wheelset-track system may occur at a frequency of f=495.01 Hz.At this time,it can be seen from the vibration mode that both the wheel treads of the wheelset bear unstable vibration.At the same time,the transient dynamic analysis method is used to extract the wheel-rail normal contact force and the vertical acceleration of the measuring point when the frictional self-excited vibration of the wheelset-track system occurs.The results show that an unstable vibration frequency with the similar value is obtained,which preliminarily verified the rationality of the finite element theoretical model.Through the effect analysis of the vertical stiffness and vertical damping of the rail fasteners on frictional self-excited vibration of the wheelset-track system,it is found that changing the vertical stiffness of the rail fasteners has little effect on the frictional self-excited vibration of the wheelset-track system,and cannot reduce the occurrence of wheel polygonal wear.However,increasing the vertical damping of the rail fasteners within a certain range can reduce the occurrence tendency of frictional self-excited vibration of the wheelset-track system,and achieve the purpose of suppressing the occurrence of wheel polygonal wear.Meanwhile,it is found that as the friction coefficient increases,the occureence tendency of frictional self-excited vibration of the wheelset-track system increases.The study also shows that the wheel polygonal wear cannot be effectively suppressed by changing the magnitude of the primary suspension force and wheel-axle interference.(2)Based on the widespread mass eccentricity of wheelsets,a vehicle-track dynamic model is firstly established to study the safety and stability of vehicles.The research results show that when the dynamic unbalance value is within a certain range,its influence on the derailment coefficient of the vehicle and the wheel load reduction rate is small,but the critical speed will decrease with the increase of the dynamic unbalance value,which seriously restricts the improvement of the vehicle running speed.As the mass eccentric phase difference increases,the critical speed of the vehicle decreases significantly,and the lateral shaking of the wheelset is severe,which will eventually lead to abnormal wear of the wheels and rails.Then,the finite element model of the wheelset-track system is established,and the dynamic response of the wheelset-track system under different operating states is studied by using the implicit transient dynamic analysis method.The research results show that when the mass eccentric wheelset rolls on the rails,the eccentric mass will increase the wheel-rail contact force,and the peak changes of the vertical contact force are more than those of the lateral force peak changes.As the speed increases,the eccentric wheelset will increase the vertical vibration energy of the wheelset-track system,and make the vibration energy in the middle-high frequency range increase significantly.When the speed v=300 km/h,the corresponding vibration frequency f=534.82 Hz becomes very prominent,which is close to the passing frequency of high-order wheel polygonal wear.At the same time,with the increase of the dynamic unbalance,the overall vibration energy of the wheelset-track system presents an increasing trend,but it has little effect on the main frequency of unstable vibration.With the increase of the eccentric phase difference of the wheelset mass,the main frequency of unstable vibration in the middle-high frequency range increases,which is likely to cause the high-order wheel polygonal wear.When the frictional self-excited vibration of the wheelset-track system occurs,the unstable vibration characteristics of the wheelset-track system corresponding to different dynamic unbalance values are similar,that is,the magnitude of the dynamic unbalance value has little influence on the frictional self-excited vibration of the wheelset-track system.At the same time,from the perspective of the excitation frequency of the wheel polygonal wear,it basically shows a trend of increasing the frequency with the increase of the running speed.Finally,when the frictional self-excited vibration of the wheelset-track system occurs,the unstable vibration is obvious in the middle-high frequency bands with the increase of the mass eccentric phase difference,and it is easy to cause the high-order wheel polygonal wear of the wheelset.(3)According to the characteristics of the polygonal wear of CRH3 EMU wheels,the frictional self-excited vibration models of the wheelset-track systems consisting of powered and trailer wheelsets are established respectively,and the effects of these two different wheelset-track systems on the wheel polygonal wear are calculated and analyzed.The research results show that when the creep force between the wheel and rail reaches a saturation state,the unstable vibration of the powered wheelset can easily cause the wheels to produce 16-17 th order polygonal wear,and the unstable vibration of the trailer wheelset can easily cause the wheels to produce 17-18 th order polygonal wear,which are basically consistent with the field measurement results of the wheel polygonal wear.When the gearbox is close to the center of the axle,the polygonal wear trend of the powered wheelset can be effectively suppressed.In addition,in the case of the coupling of the disc brake system and the wheelset-track system,the unstable vibration tendency of the wheelset-track system becomes larger,and the use of disc braking should be avoided in the high-speed operation of trains.The results show that reasonable braking force can effectively reduce the unstable vibration trend of the wheelset-track system.Finally,increasing the Young’s modulus of the brake pad material appropriately can reduce the development trend of wheel polygonal wear,and changing the Poisson’s ratio of the brake pad material has little effect on the development trend of wheel polygonal wear.(4)Based on the characteristics of the wheel polygonal wear of Lan-xin Passenger Dedicated Line,the frictional self-excited vibration models of the wheelset-track system are established,and the phenomenon of wheel polygonal wear are studied by using the complex eigenvalue method.The results show that the frictional self-excited vibration caused by the saturation of creep force between wheels and rails can easily induce 15-16 th order wheel polygonal wear on straight lines.Meanwhile,the order of the polygonal wear of wheels changes a little with the repair cycles,but the extent of the polygonal wear will become larger and larger with the decrease of the rim thickness.When the disc brake system and the wheelset-track system are coupled,the unstable vibration frequencies of the powered wheelset and the trailer wheelset easily lead to 23-24 th and 22-23 th order wheel polygonal wear,respectively.Finally,the reason why the wheel polygonal wear in winter and spring is faster than that in summer is studied.The result indicates that it is attributed to the increasing friction coefficient between the wheels and rails leads to this phenomenon. |
PDF Full Text Request